Diversity of bacterial communities in the Sundarbans Mangrove, Bangladesh, with special focus on pathogens affecting aquatic organisms

Abstract

The Sundarbans, located in Bangladesh, is the world's largest mangrove forest with a rich and diverse microbial community. The main objective of this study was to use 16S rRNA sequencing to identify the bacterial community in the Sundarban mangrove forest, particularly pathogenic bacteria to aquatic organisms. This study conducted in Bangladesh collected 225 samples of soil, water, fish, and shellfish from five locations with a typical mangrove environment. All samples underwent genomic DNA extraction, quantification, gel documentation, and subsequent sequencing. Sanger sequencing was then carried out, followed by sequencing 11 concentrated samples using the universal bacterial primer 16S rRNA. The study found 872 bacterial species, 94 genera, 38 families, and 6 phyla. Pseudomonades or proteobacteria accounted for 92% of the phylum composition, with firmicutes, bactericides, cyanobacteria, Verrucomicrobia, and actinobacteria also present at smaller percentages. Chromatiaceae had the highest species count (20.3%), followed by Ectothiorhodospiraceae (15.5%), Methylococcaceae (12.3%), Moraxellaceae (10.7%), Thiotrichaceae (8.7%), Idiomarinaceae (5.4%), and smaller groups. All the species that were identified were gram-negative bacteria and were found in different environments, mainly halophilic ones. Based on 16s rRNA sequencing, additional experimental and clinical data, as well as NCBI (BLAST), approximately 49.3% of the 872 bacterial species are typically harmless and not classified as pathogenic. The pathogenic characteristics of 24.9% of the species are still unidentified. 13.4% showed either pathogenic or non-pathogenic characteristics (a bacterium as having the potential to exhibit pathogenic or non-pathogenic characteristics in certain circumstances), while 8.4% were exclusively pathogenic, potentially capable of causing disease. Also, the bacterial species are categorized as 2.6% non-highly pathogenic (a bacterium can still have a significant impact on health, especially in weakened immune systems or other underlying health conditions), 1.3% sometimes pathogenic and 0.1% potentially pathogenic (a bacterium don't always cause disease). Sequence analysis, combination of phylogenetic, biochemical characterization (data were not shown), and other experimental validation conclude a genetic baseline of bacterial community, this research may serve as a valuable reference for future ecological and taxonomical studies as well as addressing further research scope on bacterial diversity found in the Sundarbans mangrove of Bangladesh.